configs: remove raw NAND core from k2g defconfigs

Due to previous Makefile organization, the raw NAND subdirectory was
not compiled in if CMD_NAND was not enabled. Because the Denali driver
does not compile with these boards (undefined environment offset),
remove the dependency within the defconfig over the controller driver
(was ignored anyway in the past).

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>